Effects of Low-Intensity Ultrasound on Chondrogenic Differentiation of Mesenchymal Stem Cells Embedded in Polyglycolic Acid: An in Vivo Study

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Abstract
In this study we investigated the effects of LIUS on chondrogenic differentiation of bone marrow-derived mesenchymal stem cells (BM-MSC). Our hypothesis is that LIUS may be a noninvasively effective stimulant to a biological system in vivo by turning on differentiation of MSCs and promotion of chondrogenesis. MSCs were isolated from the bone marrow of New Zealand white rabbits and cultured in monolayer for 2 weeks. They were then harvested and seeded into polyglycolic acid (PGA) non-woven mesh at a number of 5 x 10(6) cells. Cultured with a chondrogenic-defined media for 1 week, the PGA/MSCs constructs (n = 4) were implanted subcutaneously in the back of nude mice (n = 9, each group). The ultrasound (US) group received US stimulation at a frequency of 0.8 MHz and intensity of 200 mW/cm(2) for 10 min every day up to 4 weeks, while the control group had no US stimulation. Analyses of histological, immunohistochemical, biochemical, and mechanical characteristics were made at 1, 2, and 4 weeks post-stimulation, respectively. Total DNA contents showed no significant difference between the two groups. Total collagen and glycosaminoglycan (GAG) increased more significantly in the US-stimulated group than in the control. Histology of Safranin O/Fast green confirmed more intense and spreading extracellular matrix (ECM) at 2 and 4 weeks in the US-stimulated specimens. Mechanical tests exhibited that compressive strengths were also significantly higher in the US-stimulated cells at later times. This study strongly suggests that it may be possible for ultrasound to have some stimulatory effects in vivo on the chondrogenesis of MSCs.